The invention relates to dental materials based on methacrylate-modified polysiloxanes capable of polymerization.
Dental materials based on silanes capable of polymerization are known. DE 36 10 804 A1 discloses dental resin compositions which contain siloxane polymers, monomers which are co-polymerizable with the siloxane polymer, and a polymerization catalyst. The dental resin compositions are said to have an improved compressive strength, abrasion resistance and flexural strength after polymerization.
DE 34 07 087 A1 and WO 92/16183 relate to the use of compounds based on organically modified silicic acid polycondensates for coating teeth and tooth-replacement parts. The cured coats are said to be resistant to the build-up of plaque.
Dental resin compositions based on polymerizable polysiloxanes are known from DE 41 33 494, which are manufactured by hydrolytic condensation of one or several silanes of which at least one is substituted by a 1,4,6-trioxaspiro-[4,4]-nonane radical or a (meth)acrylate group, the latter preferably containing a thioether function. The dental resin compositions are said to show only a small change in volume during curing, however silanes with orthoester groups are difficult of access and less storage-stable whereas thioether groups are sensitive to oxidation.
DE 196 19 046 discloses low-shrinkage polymerizable compounds based on mercapto- or norboronnene silanes and a reaction partner for the en-thiolpolymerization. The curing of these compositions is accompanied by low polymerization shrinkage and results in products with high mechanical strength which however also contain thioether groups sensitive to oxidation.
The object of the invention is the provision of dental materials based on polysiloxanes which can be covalently incorporated in organic-inorganic composite materials and do not contain spiro- or thioether groups.
The object is achieved by dental materials which contain at least one polysiloxane based on one or several silanes according to the formula (I)
[(Wqxe2x80x94R6xe2x80x94Z)pxe2x80x94R3]mYxe2x80x94R2xe2x80x94SiXnR13xe2x88x92nxe2x80x83xe2x80x83Formula (I)
in which
Suitable heteroatoms are phosphorus and preferably oxygen.
In the whole description as well as the claims, alkyl, acyloxy, alkoxy, alkenyl groups and alkylene groups are understood to mean radicals which preferably contain 1 to 25 carbon atoms, particularly preferably 1 to 10 carbon atoms and quite particularly preferably 1 to 4 carbon atoms, and optionally carry one or several subsituents such as for example halogen atoms, nitro groups or alkyloxy radicals. Aryl means radicals, groups or substituents which preferably have 6 to 10 carbon atoms and can be substituted as stated above. The above definitions are also valid for compound groups such as for example alkyl aryl and aryl alkyl groups. An alkyl aryl group thus describes for example an aryl group defined as above which is substituted by an alkyl group as defined above.
The alkyl, acyloxy, alkoxy, alkenyl groups and alkylene groups can be straight-chained, branched or cyclic.
Preferred definitions, which can be chosen independently from each other, for the individual variables, are:
Concrete examples of particularly preferred silanes according to formula (I) are: 
The silanes of formula (I) are accessible via addition and condensation reactions known per se, the number of hydrolyzable groups, groups capable of polymerization, and further functional groups being able to be varied by the appropriate selection of educts.
Silanes in which Y has the meaning xe2x80x94NR4xe2x80x94 or N are for example accessible by addition of an aminosilane compound to an m-times unsaturated group R3: 
Thus e.g., bis[2-(2-methacryloyloxyethoxycarbonyl)-ethyl]-(3-triethoxysilylpropyl)amine is obtained by reacting 3-amino-propyltriethoxysilane with 2-acryloyloxyethylmethacrylate: 
Silanes in which Y is equal to xe2x80x94(Cxe2x95x90O)xe2x80x94NHxe2x80x94 are accessible for example by reacting an isocyanatosilane with a carboxylic acid which contains p radicals W capable of polymerization: 
The reaction of 3-isocyanatopropyltriethoxysilane with 2-methacryloyloxyethyl-hydrogen-succinate results in e.g. 2-methacryloxyethyl-3-[(3-triethoxysilyl)propylaminocarbonyl]propionate: 
Suitable carboxylic acid methacrylates can be obtained by reacting di- or tetracarboxylic acid mono or dianhydrides with suitable OH-functionalized compounds capable of polymerization such as for example 2-hydroxyethylmethacrylate or glycerine dimethacrylate.
To synthesize silanes in which Y is equal to xe2x80x94(Cxe2x95x90O)xe2x80x94NHxe2x80x94, the synthesis methods known in peptide chemistry, such as e.g. the DCC method or the mixed anhydrides method, can moreover also be used to react carboxylic acids with amino-group containing compounds, for example the reaction of an aminosilane with a carboxylic acid which contains p radicals W capable of polymerization: 
Thus, the reaction of 3-aminopropyltriethoxysilane with 2-methacryloyloxyethyl-hydrogen-succinate also results in 2-methacryloxyethyl-3-[(3-triethoxysilyl)propylaminocarbonyl]propionate: 
The silanes (I) are stable compounds and can be processed to give the polysiloxanes, either alone or together with other hydrolytically condensable compounds of silicon, aluminium, zirconium, titanium, boron, tin, vanadium and/or phosphorus. These additional compounds can be used either as such or already in pre-condensed form.
Preferred further hydrolytically condensable compounds of silicon are silanes of the general formula (II)
R7k(Zxe2x80x2R8)mSiXxe2x80x24-(k+m)xe2x80x83xe2x80x83Formula (II)
in which
Preferred definitions, which can be chosen independently from each other, for the individual variables, are:
Such silanes are described for example in De 34 07 087 A1. Particularly preferred silanes of formula (II) are: CH3xe2x80x94SiCl3, CH3xe2x80x94Si(OC2H5)3, C2H5xe2x80x94SiCl3, C2H5xe2x80x94Si(OC2H5)3, CH2xe2x95x90CHxe2x80x94Si(OC2H5)3, CH2xe2x95x90CHxe2x80x94Si(OCH3)3, CH2xe2x95x90CHxe2x80x94Si(OC2H4OCH3)3, (CH3)2SiCl2, (CH3)2Si(OC2H5)2, (C2H5)3Sixe2x80x94Cl, (C2H5)2Si(OC2H5)2, (CH3)3Sixe2x80x94Cl, (CH3O)3Sixe2x80x94C3H6NH2, (CH3O)3Sixe2x80x94C3H6SH2, 
Silanes of the general formula (II) or pre-condensed products derived from them are preferably used in a quantity of 0 to 90 mol-%, particularly preferably 1 to 60 mol-% and quite particularly preferably 1 to 40 mol-% relative to the total mass of silanes of formulae (I) and (II) or pre-condensed products derived from them.
Preferred zirconium and titanium compounds are those according to formula (III)
MeXxe2x80x3yR9zxe2x80x83xe2x80x83Formula (III)
in which
Preferred definitions, which can be chosen independently from each other, for the individual variables, are:
Particularly preferred zirconium and titanium compounds are ZrCl4, Zr(OC2H5)4, Zr(OC3H7)4, Zr(OC4H9)4, ZrOCl2, TiCl4, Ti(OC2H5)4, Ti(OC3H7)4 and Ti(OC4H9)4.
The zirconium and titanium compounds of the general formula (III) or pre-condensed products derived from them are preferably used in a quantity of 0 to 70 mol-%, particularly preferably 0 to 50 mol-% or 0 to 30 mol-% and quite particularly preferably 0 to 20 mol-% relative to the total mass of compounds of formulae (I) and (III) or pre-condensed products derived from them.
Preferred aluminium compounds are those according to formula (IV)
AlR103xe2x80x83xe2x80x83Formula (IV)
in which
R10 stands for a halogen atom, a hydroxyl or C1 to C8-alkoxy group, preferably for a halogen atom or a C1 to C5-alkoxy group.
Particularly preferred aluminium compounds are Al(OCH3)3, Al(OC2H5)3, Al(OC3H7)3, Al(OC4H9)3 and AlCl3.
The aluminium compounds of the general formula (IV) or pre-condensed products derived from them are preferably used in a quantity of 0 to 70 mol-%, particularly preferably 0 to 30 mol-% and quite particularly preferably 0 to 20 mol-% relative to the total mass of compounds of formulae (I) and (IV) or pre-condensed products derived from them.
In addition, complexed compounds of zirconium, titanium and aluminium can be used, acids and xcex2-dicarbonyl compounds being preferred as complexing agents. Preferred acids are acrylic and methacrylic acids or other methacrylate carboxylic acids such as e.g. 2-methacryloyloxyethyl hydrogen succinate or the 1:1-adducts of glycerine dimethacrylate and carboxylic acid anhydrides, such as e.g. succinic acid or phthalic anhydride. Preferred xcex2-dicarbonyl compounds are acetylacetone, acetoacetic acid ethyl ester and in particular 2-acetoacetoxyethyl methacrylate. These complexing agents are preferably reacted with alkoxy derivates of zirconium, titanium or aluminium in the molar ratio of 1:1.
In addition, boron trihalides, stannic tetrahalides, stannic tetraalkoxides and/or vanadyl compounds are suitable for co-condensation with the silanes according to formula (I).
When using additional hydrolytically condensable compounds, the proportion of silanes according to formula (I) in the polysiloxanes is preferably 10 to 99 mol-%, particularly preferably 40 to 99 mol-%, each relative to the initial monomer compounds. The proportion of silanes (I) and (II) together is preferably at least 20 mol-%, particularly preferably at least 80 mol-%, likewise relative to the initial monomer compounds.
The manufacture of the polysiloxanes is carried out by hydrolytic condensation of the above-listed compounds. In the case of the silanes of the general formulae (I) and (II), the hydrolyzable groups X are first split off, silanoles, silane diols and silane triols being obtained which condense to polysiloxanes with an inorganic network of Sixe2x80x94Oxe2x80x94Si units accompanied by splitting-off of water.
The hydrolytic condensation of the silanes generally takes place by reacting the silicon compound to be hydrolized, either directly or dissolved in a suitable solvent, at room temperature or accompanied by slight cooling, at least with the quantity of water stoichiometrically required for complete hydrolysis and stirring the resulting mixture for one or several hours. Aliphatic alcohols such as for example ethanol or isopropanol, dialkyl ketones such as acetone or methylisobutyl ketone, ethers such as for example diethyl ether or tetrahydrofuran (THF), esters such as for example ethyl or butyl acetate and mixtures thereof are in particular suitable as solvents.
The hydrolysis and condensation of the initial mixture preferably takes place in the presence of a condensation catalyst, with compounds splitting off protons or hydroxyl ions, such as organic or inorganic acids or bases, and also compounds releasing fluoride ions, such as ammonium fluoride or sodium fluoride, being preferred. Particularly preferred are volatile acids or bases, in particular hydrochloric acid or ammonia. During the hydrolysis and condensation, it has proved worthwhile to adopt sol-gel techniques, as described for example in C. J. Brinker et al., xe2x80x9cSol-Gel-Sciencexe2x80x9d, Academic Press, Boston, 1990.
If the hydrolytic condensation is carried out in the presence of zirconium, titanium or aluminium compounds, the water is preferably added stepwise, the temperature preferably being kept in the range of approximately 0 to 30xc2x0 C. It is often advantageous to add water in the form of hydrous solvents such as for example aqueous ethanol, or to produce it in situ, for example by chemical reactions such as esterifications.
The polysiloxanes obtained can be used directly or after partial or complete removal of the solvent. It is often advantageous to replace the solvent used for the hydrolytic condensation with another solvent. The silanes (I) and in particular the polysiloxanes show only a low volatility because of their high molecular weight and therefore can largely be processed safely. With regard to the mechanical properties of the polysiloxanes, it is advantageous to perform the hydrolytic condensation up to a degree condensation of 65 to 95 mol-%, the degree of condensation being able to be measured by 29Si-NMR.
The complete curing of the polysiloxanes takes place by the addition of suitable initiators and optionally further components capable of polymerization by thermal, photochemical or redox-induced polymerization. Several curing mechanisms, e.g. radical and cationic polmerization, can also be used simultaneously or in successive steps when different groups capable of polymerization, e.g. (meth)acryl and epoxide groups, are present.
To initiate the radical polymerization, thermal and/or photoinitiators are preferably used.
Preferred initiators for the thermal curing are peroxides such as for example dibenzoyl peroxide, dilauryl peroxide, tert.-butylperoctoate and tert.-butylperbenzoate as well as azobisisobutyroethyl ester, benzpinacol and 2,2-dimethylbenzpinacol.
Preferred photoinitiators are benzophenone and benzoin as well as their derivatives, xcex1-diketones and their derivatives such as for example 9,10-phenanthrenequinone, diacetyl and 4,4-dichlorobenzil. Particularly preferred photoinitiators are camphorquinone and 2,2-methoxy-2-phenyl-acetophenone and in particular combinations of xcex1-diketones with amines as reducing agents such as for example N-cyanoethyl-N-methylaniline, 4-(N,N-dimethylamino)-benzoic acid ester, N,N-dimethylaminoethyl methacrylate, N,N-dimethyl-sym.-xylidine or triethanolamine. In addition, acylphosphines such as for example 2,4,6-trimethylbenzoyldiphenyl or bis-(2,6-dichlorobenzoyl)-4-N-propylphenyl phosphinic oxide, are suitable as photoinitiators.
Diaryliodonium or triarylsulfonium salts such as for example triphenylsulfoniumhexafluorophosphate and triphenylsulfoniumhexafluoroantimoniate are particularly suitable for the dual curing of radically and cationically polymerizable systems.
Redox initiator combinations such as for example combinations of benzoyl or lauryl peroxide with N,N-dimethyl-sym.-xylidine or N,N-dimethyl-p-toluidine are used as initiators for a polymerization at room temperature.
The polymerization of polysiloxanes with 2 or more (meth)acrylate radicals results in three-dimensional organic networks, in which the mechanical properties such as for example strength and flexibility, as well as the physico-chemical properties of the cured materials such as for example adhesivity, water absorption and refractive index, can be varied via the distance between the Si atoms and the (meth)acrylate radicals capable of polymerization, i.e. via the length of the spacer group xe2x80x94R2xe2x80x94Yxe2x80x94R3xe2x80x94Zxe2x80x94R6xe2x80x94, as well as via the presence of further functional groups, and optimally matched to the requirements of each application case. The use of aliphatic groups as spacers results in relatively flexible, and the use of aromatic groups relatively rigid products.
The crosslinking density of the cured materials can be set by the number of (meth)acrylate groups capable of polymerization, which allows a further influencing of the properties and possible uses of the polysiloxanes.
If the monomeric silanes contain, in addition, ionically crosslinkable groups such as for example epoxide or oxethane groups, a further increase in the crosslinking density can be achieved by their simultaneous or subsequent ionic polymerization.
The polysiloxanes can be used mixed with suitable ionically and/or radically polymerizable mono- or multifunctional monomers. Preferred monomers are mono(meth)acrylates, such as methyl, ethyl, butyl, benzyl, furfuryl or phenyl (meth)acrylate, multifunctional acrylates and methacrylates such as for example bisphenol-(A)-di(meth)acrylate, bis-GMA (an addition product of methacrylic acid and bisphenol-A-diglycidyl ether), UDMA (an addition product of 2-hydroxyethyl methacrylate and 2,2,4-hexamethylene diisocyanate), di-, tri- and tetraethylene glycol-di(meth)acrylate, decanedioldi(meth)acrylate, trimethylol propane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate and butane diol-di(meth)acrylate, 1,10-decanediol-di(meth)acrylate or 1,12-dodecanediol-di(meth)acrylate.
The polymerizable monomers are preferably used in a quantity of 1 to 80 wt-%, particularly preferably 5 to 50 wt-% and quite particularly preferably 5 to 30 wt-% relative to the total mass of polymerizable monomer and silanes of the formula (I) or pre-condensed products derived from them.
The mixtures can moreover contain further additives such as colorants (pigments and dyes), stabilizers, flavoring agents, microbiocidal active ingredients, plasticizers and/or UV absorbers.
Furthermore, to improve the mechanical properties, the compositions can be filled with organic or inorganic particles or fibres. Preferred inorganic particulate fillers are amorphous spherical materials based on mixed oxides of SiO2, ZrO2 and/or TiO2 (DE 40 29 230 Al), microfine fillers such as pyrogenic silicic acid or precipitation silicic acid as well as macro- (particle size 5 xcexcm to 200 xcexcm) or minifillers (particle size 0.5 to 5 xcexcm) such as quartz, glass ceramic or glass powders with an average particle size of 0.5 xcexcm to 5 xcexcm as well as X-ray opaque fillers such as ytterbium trifluoride. In addition, glass fibres, polyamide or carbon fibres can also be used as fillers.
The compositions are in particular suitable as dental materials such as adhesives, coating materials, dental cements and filling materials.
The dental materials according to the invention preferably contain
(a) 5 to 99.9 wt-%, preferably 5 to 90 wt-%, particularly preferably 10 to 70 wt-% polysiloxane; and
(b) 0.1 to 5.0 wt-%, preferably 0.2 to 2.0 wt-% polymerization initiator; and preferably
(c) 1.0 to 80 wt-%, preferably 5.0 to 50 wt-% ionically and/or radically polymerizable monomer; and preferably
(d) 1.0 to 90 wt-%, preferably 2.0 to 80 wt-% fillers.
The figures given are in each case relative to the total mass of the dental material.
In the following, the invention is explained in more detail with reference to embodiments.